The present invention relates to an apparatus for controlling the intermittent and reciprocating movements of a fabric supporting carriage, which is required to carry out stitching lines according to prefixed patterns or designs in a quilting or embroidering machine. Quilting machines perform the stitching according to a particular pattern or design of two or more superimposed fabrics with insulating material therebetween. The product so obtained has several different applications, e.g. in manufacturing bed covers, sleeping bags, mattresses, etc. Such quilting machines include driving rolls for the fabrics and the insulating materials, a fabric-supporting carriage able to move transversally to the advancement direction of said rolls and one or more, vertically movable needle-bearing bars. Stitching is preformed during the time intervals when the fabrics are still, whereas when the needles are lifted, the fabrics are longitudinally advanced by means of the driving rolls and transversally shifted by the reciprocating movements of the fabric-bearing carriage.
A considerable shortcoming of the known cam-operated quilting machines is that only limited sizes and numbers of the stitched design can be obtained because the non-rectilinear stitching is carried out through the composition of the relative advancing movements of the fabric and the lateral movements of the fabric-bearing carriage. Both of these movements are rectilinear and orthogonal with respect to one another and it is therefore obvious that the shape of the stitching and the distances between stitches can only be varied by changing the relative speed of the two movements (and therefore the entity of the movements).
Whereas there is no particular difficulty in controlling the driving rolls the two-way variable-length jerking movement of the fabric-bearing carriage imposes considerable limitations to the performance of the quilting machine.
There are known apparatuses for controlling the carriage employing step by step electric motors (associated with hydraulic systems to increase the torque) or variously shaped cams which effect only a specific movement amplitude and contour. These control systems and shortcomings due to the mounting clearance of cams and rolls, machine noise, wear of the components and above all, a complete lackness of flexibility of the stitching patterns. In fact it is a matter of course that a cam, however accurately designed, cannot be used but for a limited number of stitching patterns even if in combination with sophisticated programming systems which in any case do not avoid the change of the cam for each type of pattern. It is moreover impossible to effect a gradual shift from one shape of stitching to another, there being upper limits for the maximum length of the run and lower limits for the minimum allowable inversion of movement, and finally it is necessary to stock a number of cams suitable to the production requirements.